Mobile devices have become ubiquitous in today's world and are increasingly used to access various communication services (e.g., voice calls, video calls, messaging, streaming multimedia content, playing high definition online games, and so forth) over wireless communication networks. A wireless communications network may include a number of base stations (BS's), each supporting communication for a number of mobile devices or user equipment (UE's). A UE may communicate with a BS via downlink and uplink. The downlink (or forward link) refers to the communication link from the BS to the UE, and the uplink (or reverse link) refers to the communication link from the UE to the BS. Further, the wireless communication networks may correspond to multiple-access networks capable of supporting multiple users (i.e., UE's) by sharing the available network resources (e.g., time, frequency, and power).
Conventional third generation (3G) and fourth generation (4G) wireless communication networks employ various orthogonal multiple access (OMA) as multiple access techniques, such as code division multiple access (CDMA) in 3G, and frequency division multiple access (FDMA) or time division multiple access (TDMA) in 4G. OMA techniques involve transmitting to multiple UE's with full power. The transmission is based on splitting resources such as frequency in FDMA, the code in CDMA, or time in TDMA. Such a division is intended to increase the number of UE's that can be catered to by the BS's. However, the ability of OMA technologies to meet exponentially increasing demand for mobile data is limited and the existing wireless communications networks are increasingly getting congested. Advance wireless communication networks (advance 4G or 5G) employing multiple access techniques, such as non-orthogonal multiple access (NOMA) have the potential of meeting the demand of increasing UE's and the quality of service (QoS) requirements, which are outstripping the ability of the aforementioned OMA technologies.
NOMA is a multiple access technique for encoding signals in wireless communication that enables several users to use the same frequency bandwidth that is differentiated by the power allocated for each user. NOMA includes generation of codewords from a multi-dimensional codebook by using sparse code multiple access. NOMA further includes a combination of mapping quadrature amplitude modulation (QAM) symbol and spreading, wherein incoming bits are directly mapped to multi-dimensional codewords of codebook and spread over multiple sub-carriers. The same codeword may be applied or assigned to different UE's. Each UE corresponds to each layer, which stores codeword from one codebook. Thus, NOMA provides the mechanism for multiplexing different layers (i.e., signal for different UE's) during transmission of signals by the BS. The decoding technique in case of NOMA employs use of successive interference cancellation (SIC) to detect the signals of users with lower powers. As will be appreciated, codeword is data encoded using an error correcting code such as using a cyclic redundancy code (CRC). Further, as will be appreciate, a codebook is generated by partitioning multiple codewords and assigning indices to the codewords. The codebook correlates the codewords in complex vector space. Compared to the existing technologies, NOMA provides higher network capacity (up to 1000 times current network capacity), better connectivity (up to 100 times current number of device used), higher data rate (up to 100 times current packet data rate), reduced network latency (less than 1 ms) at lower cost, higher energy efficiency, and enhanced robustness.
However, existing techniques for providing NOMA has a number of limitations. For example, existing techniques provide for assignment of distinct codewords from codebook to each UE in the coverage area under NOMA. However, the limited number of codewords may get exhausted in case of number of UE's in the coverage area and those seeking admission into the coverage area exceeds the available number of codewords. Further, such scenarios may result in undesired admission refusal of the UE's. In other words, existing techniques are limited in supporting large number of UE's because of the distinct codeword assignment to each UE that may impact the service allowance of UE's. Additionally, existing techniques fail to provide mechanism for appropriate codeword assignment for supporting multiple MCS simultaneously under NOMA. The BS uses a mechanism for multiplexing signals for each UE with distinct codeword for signal transmission for a specific MCS. However, this may impact multiplexing of transmitted signals for multiple MCS simultaneously and may further aggravate inter cell interference. Further, existing techniques fail to provide mechanism for interference avoidance or mitigation among transmitted signals for UE with similar assigned-codeword or pattern within close proximity. This may increase SINR impacting quality of signal reception by UE's. In other words, codeword assignment is NOMA based without supporting use of multiple MCS simultaneously and without considering interference avoidance among neighboring UE's. Moreover, existing techniques provide for signal power allocation based on dynamically determined relative channel quality of individual UE's or UE-clusters, thereby requiring frequent change in such determination due to UE-mobility. This may lead to inappropriate allocation of signal power to UE's and/or UE-cluster. The issue gets further aggravated with increased number of UE's in the coverage area and with extent of mobility of the UE's in the coverage area.